Electro-deposition of tin



Patented Jan. 15, 1935 PATENT OFFICE i ELECTED-DEPOSITION 0F TIN Paul R. Pine, Elyria, Ohio, assig-nor to The Harshaw Chemical Company, Cleveland, Ohio,

a corporation of Ohio No Drawing. Application January 28-, 1933, Serial No. 654,113

9 Claims. (01. 204 -17) While electro-plating with tin is practiced commercially, there are essential limitations which handicap its use. Close control has been necessary, the current density permissible has been of restricted range, and While various bath compositions have been suggested, general practice has settled on an alkaline type of bath based,

on sodium stannate. A procedure which can permit bath variation over wide ranges, and which allows deposition of a dense thick coating of fine structure at a high rate of speed, and which does not critically require low current densities, is accordingly an important desideratum.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described, and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative however, of but a few of the various.

ways in which the principle of the invention may be employed.

In its general aspects, the invention contemplates electro-deposition in an acid type of bath, employing the sulphate, and controlled by an agent which I designate a soluble resin or cresolresin. The anode employed may be tin in suitable form, as for instance commercially pure tin, and the cathode may be of any suitable or desired form, depending upon whether a mere coating or a built-up deposit is contemplated. The present process allows deposition not only on iron,.steel, copper, and other metals or their I alloys low in the electromotive series, but is also feasibly operative upon zinc, aluminum, and other metals or their alloys high in the electromotive series.

With a bath for example of stannous sulphate, and free acid, as sulphuric acid, I incorporate a control agent of a soluble resin character, and desirably of synthetic origininvolving conjugation of phenolic radicles by an organic condensing compound. Such an agent may be made for instance by reaction between refined cresol, from which all o-cresol has been removed, and such compounds as an aldehyde as formaldehyde, or gelatin, aloin, etc., and sulphuric acid. While a highly purified form of gelatin may be employed, practically the less purified forms such as glue may be applied. In the detail preparation of this control agent, I may for example, soften a calculated quantity of glue to a rubbery consistency with the smallest quantity of water, and stir into and heat in an excess of refined ,plete.

cresol from which the o-cresol has been removed, and constituting essentially then a mixture of meta-cresol and para-cresol. The mixture is heated to not above C. until reaction is com- Thereupon, a calculated amount of con-. centrated sulphuric acid is added, and the whole is heated to not over 110 C.

As another example of convenient procedure for the preparation of the control agent, a vdesired amount of gelatin is treated with a calculated quantity of concentrated sulphuric acid, at a temperature not over C. and is allowed to stand'until waste matter rises to the top as scum. This is removed. An amount of refined cresol corresponding in quantity to the gelatin is separately treated with an equi-molecular amount of sulphuric acid at a temperature not over C. for a minimum of one-half hour.

The two solutions are cooled to about 10 C. and are then mixed carefully such that the heat of reaction does not carry the temperature higher than about 60 C. The reaction product is a water-soluble material containing little inert matter. If however, the temperature of the reaction were allowed to rise to 80-100 C., the product would be of different and unsuitable character by reason of the secondary reaction occurring.

With suitable conditions of agitation etc., and a bath of stannous sulphate, sulphuric acid, and my soluble resin control agent, it is possible to deposit tin in relatively great thickness, such as over two thousandths of an inch and more, and the current densities may run as high as 100 amperes per square foot of surface, and the tin is deposited in a dense fine semi-mirror surface such as has not heretofore been possible.

I have additionally discovered that by incorporating a fluoride in small amount, such as sodium fluoride, a harder surface results. As a still further refinement of theinvention, I have also discovered that by the incorporation of a small amount of a nickel salt, such as nickel sulphate, or nickel fluoride, a smoother still more desirable .surface is obtained. The plating bath as preferably used then, may have such a composition as the following, it being understood that the last two ingredients are optionally added for results more desirable for certain usages.

NiSO4 .3-

In the art heretofore it has been known to employ simple molecule compounds, such as cresol per se, but no one so far as I am aware has employed a large molecular conjugate such as contemplated in the present invention, and which I have found has opened up the way to elimination of vexatious critical characteristics in electrodeposition baths. In accordance with my process,

thus, operation may be carried on with very little special control. No sulphuric acid or tin sulphate need be added except to compensate for drag-out losses, and the soluble resin control agent is long-lived. The bath will operate on continuous service without constant attention, and the composition may in fact vary over wide ranges without affecting the result. A much lower free acid concentration may in fact be used than has heretofore been practical with acid type baths. The acid may fall as low as 6 ounces per gallon, and the bath still function perfectly. Nor does deterioration occur in the event that the solution is left standing idle. Under normal usage, the general efliciency developed is 96-98 per cent and the throwing power is excellent.. The solution may be operated at temperatures of 20 C.- C., and current densities of 10-100 amperes per square foot. It correspondingly incurs a low power cost. And unlike prior practice, the plating of tin upon zinc and other like metals and alloys now becomes practicable.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided thefeatures stated in any of the following claims, or the equivalent of such, be employed.

I therefore particularly point out and distinctly claim as my invention:-

l In a process of the character described, passing a plating current between a tin anode and a desired cathode in a solution of tin sulphate and sulphuric acid, there being added to such solution a soluble cresol resin.

2. In a process of the character described, passing'a plating current between a tin anode and a desired cathode in a solution of tin sulphate, and sulphuric acid, there being added to such solution a soluble cresol-gelatin resin.

3. In a process of the character described, passing a plating current between a tin anode and a desired cathode in ,a solution of tin sulphate, and sulphuric acid, there being added to such solution a soluble cresol-aloin resin.

4. In a process of the character described, passing a plating current between a tin anode and a desired cathode in a solution of tin sulphate, and sulphuric acid, there being added to such solution a soluble cresol-formaldehyde resin.

5. In a plating bath, the combination of tin sulphate, sulphuric acid, and an added soluble resin, prepared from refined cresol and a reagent selected from the group consisting of gelatin, aloin, and a reactive aldehyde.

6. As an addition agent in sulphuric acid tin electro-deposition, a soluble cresol resin.

'7. As an addition agent in sulphuric acid tin electro-deposition, a soluble cresol-gelatin resin.

8. As an addition agent in sulphuric acid tin ele'ctro-deposition, a soluble cresol-aloin resin.

9. As an addition agent in sulphuric acid tin electro-deposition, a soluble cresol-formaldehyde resin.

PAUL R. PINE. 

